Aids could slash the wealth of some African countries by as much as 20%, according to evidence presented at the International Aids Conference in Durban.

Researchers warn of a vicious cycle in which HIV/Aids drives many families into deepening poverty, and at the same time poverty speeds the spread of HIV.

The world has never seen a problem of this magnitude

Callisto Madavo, World Bank Vice-President

"Breaking this cycle will require not only greatly increased investments in more effective HIV prevention and care, but also more effective measures to combat poverty," said Robert Hecht of the United Nations Aids programme.

There are nearly 25 million people in Africa infected with the HIV virus that can lead to Aids - 75% of the world's infected people.

The findings on the economic costs of the epidemic were presented at an international meeting of economists, which was held as part of the Durban conference.

Callisto Madavo, World Bank Vice-President for Africa told the meeting: "The world has never seen a problem of this magnitude.

"The need to know more about the economic causes and consequences of the epidemic, and how donor countries and governments in the developing world can work together to prevent new infections and help people who are already ill."

Resources cut

Studies presented to the meeting suggest that high levels of HIV infection reduce growth significantly, making it harder for countries to fight poverty and to create the resources to cope with the epidemic.

Delegates called for more investment in Aids education

In South Africa, where an estimated 20% of the population is infected with HIV, researchers forecast that GDP will be 17% lower by 2010 than it would have been without an epidemic.

Individual families will also find their incomes reduced.

Botswana - which has the world's highest incidence of HIV, with 36% of its population infected - was warned that it faces "a rapid increase in the number of very poor and destitute households in the coming decade".

Although income from diamond exports will cushion the impact on GDP growth, the poorest households will be 13% worse of, the study said.

Aids causes lasting damage to poor children who are orphaned as one or both parents succumb to HIV, studies suggested.

A study in Zambia found that 65% of the households in which the mother had died dissolved, with the children usually going to live with elderly female relatives who were themselves unable to provide adequately for the children.